New approach to requirements trade-off analysis for complex systems

We propose a faceted requirement classification scheme for analyzing heterogeneous requirements. The representation of vague requirements is based on L.A. Zadeh's (1986) canonical form in test score semantics and an extension of the notion of soft conditions. The trade-off among vague requirements is analyzed by identifying the relationship between requirements, which could be either conflicting, irrelevant, cooperative, counterbalance, or independent. Parameterized aggregation operators, fuzzy and/or, are selected to combine individual requirements. An extended hierarchical aggregation structure is proposed to establish a four-level requirements hierarchy to facilitate requirements and criticalities aggregation through the fuzzy and/or. A compromise overall requirement can be obtained through the aggregation of individual requirements based on the requirements hierarchy. The proposed approach provides a framework for formally analyzing and modeling conflicts between requirements, and for users to better understand relationships among their requirements.